Part 3: Lewis Dot Structures and Multiple Bonds

Objectives• To learn how to depict covalent

bonds with Lewis Dot Structures• To understand the difference

between single, double, and triple covalent bonds

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H + H H2 + energy

atom atom molecule

Molecule has less energy and is more stable than atoms

Stability in Bonding

Ways to represent the hydrogen molecule:

• H2 molecular formula - indicates number of atoms in molecule

• H-H structural formula - dash is 1 SHARED pair of electrons

• H:H dot structure (Lewis structure) - use 1 dot for each electron in highest energy level

Covalent Bonding

• Covalent bonding is the sharing of electrons between atoms

• Because of this, the atomic orbitals of atoms overlap one another

Crude picture representation: . . ATOMIC orbitals overlapping

Refined picture representation: . . MOLECULAR orbital -

holds 2 electrons maximum

Orbitals can not overlap completely because of the 2 nuclei

Orbital Overlap

Lewis Dot Structures of Covalent Compounds

• Electrons of an atom are either core or valence electrons

• Valence electrons are the outermost and involved in chemical reactions

• They are shown in Lewis Dot structures

• Valence electrons vary by element• Main Group element’s valence

electrons are equal to their group number

• Ex: Sodium (Na) belongs to Group 1A and therefore has 1 valence electron.HLi

KRbCs

NaBeMgCaSrBa

BAlGaInTi

CSiGeSnPb

NPAsSbBi

OSSeTePo

FClBrIAt

HeNeArKrXeRn

Transition metals

IA

IIA IIIA IVA VA VIA VIIA

VIIIA

Valence Electrons

How many valence electrons does Potassium (K) have? 1

How many valence electrons does Antimony (Sb) have? 5

How many valence electrons does Phosphorus(P) have? 5

How many valence electrons does Magnesium (Mg) have? 2

Let’s Do It!!!

HeNeArKrXeRn

VIIIA • Noble Gases in Group VIIIA have either two valence electrons (He) or eight (Ne, Ar, Kr, Xe, and Rn)

• They are extremely stable and this is the basis for the Octet Rule - elements react to attain the electron configuration of Group VIIIA

Noble Gases

Neon has eight valence electrons, so its Lewis dot symbol is:

Ne

• Remember metals on the left of the periodic table tend to lose electrons and nonmetals on the right tend to gain

• This is to achieve a stable configuration of 8 valence electrons

Octet Rule

• Each fluorine atom has seven valence electrons and require one more electron to satisfy the Octet Rule.

F F

Covalent Bond

F F• The left fluorine has a total of eight

electrons and the right fluorine has a total of eight valence electrons

• Nonmetallic elements react together and share electrons in order to obtain eight valence electrons

FF

Covalent Bond

• The two electrons in the covalent bond are often represented by a line

• The F2 molecule can be represented using a line (bonding pair) and dots (six lone pairs)

FF

Covalent Bond

• Some atoms have to share more than one electron in order to meet the Octet Rule

• Each oxygen atom has six valence electrons and they each require two more electrons to satisfy the Octet Rule

O O

Multiple Covalent Bonds

• Both the left and right atoms now have a total of eight

• A double bond is represented by two single lines and each represents two electrons

O O

O O

Multiple Covalent Bonds

• Hydrogen is an exception to the Octet Rule because it only needs two electrons to be stable

H F• H has one valence

electron and it requires one more

• F has seven valence electrons and it requires one more

H F

Covalent Bonds

H F• The hydrogen atom now has a total of

two electrons around it and is stable• The fluorine atom now has a total of

eight electrons around it and is stable

Covalent Bonds

Objectives• To learn how to depict covalent

bonds with Lewis Dot Structures• To understand the difference

between single, double, and triple covalent bonds

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